Such a frame collapsible and extendable by means of a turning movement is known from EP-A-0 476 729. Two successive upright elements are interconnected herein by a hinge joint in the form of a linear joint which, to avoid clearance in the extended position, only permits changes of angle between the upright elements. However, for the upright elements to be able to move between the collapsed and extended positions, they must be able to twist, which is achieved by using a steel U-section. This does not alter the fact, however, that during each collapsing and extending movement not only the upright elements but all the linear joints between the upright elements are subject to twists which, in fact, constitute undesirable tensions and can still lead to clearances which negatively affect the stability. The linear joints must not only be robust but also be secured in the extended position against spontaneous bending back and/or through. To this end, various measures have been taken for both the hinges between two upright elements and the joints between an upright element and a supporting frame. From a structural point of views all this makes the frame relatively complicated and expensive, while the easily twisted upright elements cause the stiffness of the extended frame to be inferior.
Such a frame is particularly meant as a display rack for exhibitions and the like. This relatively weak structure makes an unreliable impression there and is unsuitable for this very reason. Besides, the hinges and the steel U-sections remaining visible results in poor aesthestics, which further adversely affects the serviceableness of the frame.
It is an object of the invention to improve a frame described in the opening paragraph so as to obtain a frame looking relatively stiff and robust in the extended position, while avoiding, during collapsing and extending, twists causing additional wear and not compensated by a displacement.